Magnetic attraction and repulsion is commonly employed as a motive force to operate devices such as valve closure members, pistons in cylinders to achieve a pumping action, and contactors and switches for opening and closing electrical circuits.
Such drives may have a bistable or monostable characteristic, and often employ a spring force to provide a restoring force and create a monostable operating characteristic.
Magnetic fields to achieve the operation are usually generated by causing an electric current to flow in a winding surrounding a ferromagnetic core or the like, which if the magnetic field is to collapse when the current flow ceases (as is usually required), is usually constructed from a magnetisable material having a low magnetic permanence.
Where valves control the flow of inflammable or poisonous gases or fluids, it is usual to design the magnetic drive therefor to be monostable and to have a so-called fail-safe characteristic in the event of a power failure. By fail-safe is meant that the valve will revert to a closed condition in the event that there is an electrical power failure.
Devices incorporating the invention obviate the need to provide electric current continuously to maintain the operational state of the device which may have a monostable or bistable characteristic.